1. Field of the Invention
The present invention relates to a low-cost solar cell with high conversion efficiency.
2. Description of the Prior Art
Present-day solar cells are made from a variety of Group IV materials (such as single-crystal silicon, polycrystal silicon, .amorphous silicon, amorphous SiC, amorphous SiGe, and amorphous SiSn), Group III-V materials (such as GaAs, AlGaAs, and InP), and Group II-VI materials (such as CdS, CdTe, and CU.sub.2 S). They also come in varied structures, such as pn structure (including that of back surface field), pin structure, heterojunction structure, Schottky structure, tandem type, and multijunction structure (including that of vertical junction).
Solar cells are required to have a high conversion efficiency, to be produced at a low cost, and to recover their production cost in a short period. These requirements have not been met so far. A solar cell of single-crystal silicon or polycrystal silicon has a high conversion efficiency but takes a long time (more than 10 years) to recover its production cost. A solar cell of amorphous silicon is produced at a low cost (and hence recovers its production cost in a short period) but is poor in conversion efficiency. A solar cell of GaAs has a high conversion efficiency but is more expensive than that of single-crystal silicon, and hence its use is limited. At present, there are no solar cells that meet the contradicting requirements: high conversion efficiency and low production cost.